Many methods of making gears are known in the art. For example, one method involves the use of mechanical or isostatic pressing to compact powdered metal into a gear shape having a desired density. The powdered metal gear shape is then heat treated or sintered to impart certain characteristics, such as improved hardness, to the gear. Finally, the gear can be forged with known forging equipment to further increase density. Gear manufacture processes such as this are described in U.S. Pat. Nos. 3,394,432, 3,842,646, 3,891,367, 4,470,953, 4,585,619 and 4,710,345. U.S. Pat. No. 4,708,912 discloses a gear manufacturing process which utilizes a blank instead of powdered metal, and U. S. Pat. No. 3,752,003 discloses a method of making a composite gear. Conventional methods exist to modify the above-described gear manufacturing processes to obtain gears with hardened surfaces, as disclosed in U.S. Pat. Nos. 3,398,444 and 4,885,831 .
Certain gear shapes, such as helical gear shapes, present problems that render production of such gears by the conventional processes described above very difficult and very costly. It would be desirable to develop a process for manufacturing these gear shapes which would allow for the use of certain composite materials which would produce the desired response to rapid heat treatment, such as by induction.
It would also be desirable that the composite materials at the same time possess the needed properties of hardness and residual stress profile for superior performance in bending and contact fatigue. Still further, it would be desirable to develop a method of gear manufacture which allows for the placement of special wear resistant layers at specified points on the gear.